Reprinted from the A.C.E.C. BBS (614)-471-8559
If I were allowed only one computer, I think that I would prefer
a 1200XL. Only two features draw me toward the 800XL or the 130XE,
the Parallel Buss and the quality of the video on my 1702 Commodore.
The 130XE makes the 1200XL screen look like I'm using a television -
through the tuner! Oddly enough, the 1200XL has almost a dozen
transistors in it's video circuits, while the XE only has 3 or 4.
Yet, the 130XE has a much, much better output. (same transistors,
same signal source.... did the Warner engineers get paid by the
component???) Nice for us, though. We can just duplicate the XE
circuitry in the 1200XL - which is exactly what I will describe in
this article. The result is a picture that is just as clear as the
one from a 130XE and costs almost nothing. This is designed for a
separate CHROMA system like the 1702. There is no provision for
output to a television or a composite monitor.
Installation will consist of removing certain components and
either replacing them with another part, replacing them with a wire,
or not replacing them at all. One component has to be added at a
point in the circuitry where no component now exists. All others are
mounted in existing locations.
REMOVE REPLACE WITH
R21 22K 1.5K
L15 820uh wire
C115 10uf wire
C60 100pf ----
R187 1meg 2.2K
CR20 1N4148 ----
R22 4.3K ----
R23 180 47
R24 180 100
R25 130 ----
R28 130 wire
C62 10pf ----
R180 180 ----
R181 3.3K 6.8K
C118 100pf wire
R182 6.2K ----
R183 2.2K ----
R184 1K wire
R185 1K 180
C119 3.9pf ----
CR19 1N4148 150ohm resistor
C116 .001uf ----
Add a 47ohm resistor between the collector of Q11 and +5volts.
You will have to cut the foil right next to the pad to isolate the
collector. Solder a wire from the junction of CR19 (now a 150ohm
resistor) and R180 (removed) to the unused pin on the monitor socket.
This is the new CHROMA source. Pull out Q7, Q8, Q16, Q17, and Q18.
Check all of your changes very carefully. Measure the resistance
between +5volts and ground to make sure that you haven't got any
power supply faults. (It should read over 100ohms) Power up in
self-test mode and correct the color by adjusting R48.
You are now only missing the Parallel Buss.....